Polycarboxylic acid-bridged thio-methylenephenol antioxidants

ABSTRACT

THIOMETHYLENE PHENOL COMPOUNDS ARE PROVIDED WHEREIN FROM TWO TO FOUR HINDERED PHENOL RADICALS HAVING THIOMETHYL SUBSTITUENTS META TO THEIR HYDROXY GROUPS ARE JOINED, EITHER DIRECTLY OR THROUGH INTERPOSED ETHOXY GROUPS, TO THE CARBONYL RADICALS OF AN ORGANIC POLYCARBOXYLIC ACID. THESE COMPOUNDS HAVE THE FORMULA:   ((2,6-DI(CH3-),3-HO,4-R-PHENYL)-CH2-S-(CH2-CH2-O)Z-CO-)N-Y   WHEREIN R IS A BRANCHED CHAIN ALKYL GROUP CONTAINING THREE TO ABOUT TWELVE CARBON ATOMS, Z IS ZERO OR ONE, N IS 2, 3, OR 4, AND Y IS THE RESIDUE OF THE ORGANIC CARBOXYLIC ACID Y(COOH)N. THEY ANTIOXIDANTS FOR OXYGEN-SENSITIVE ORGANIC MATERIALS, PARTICULARLY POLYOLEFINS OF 2-6 CARBON ATOMS SUCH AS POLYPROPYLENE PLASTICS. THEY ARE PREPARED BY CONDENSING FROM 2 TO 4 MOLES OF A 3MERCAPTOMETHYL-2,4-DIMETHYL - 6 BRANCHED-CHAIN ALKYLPHENOL WITH THE CHLORIDE OR BROMIDE OF AN ORGANIC DICARBOXYLIC, TRICARBOXYLIC OR TETRACARBOXYLIC ACID, PREFERABLY IN THE PRESENCE OF AN ACID ACCEPTOR, OR BY FIRST CONDENSING THE CORRESPONDING 3-CHLOROMETHYLPHENOL WITH 2-MERACPTO ETHANOL AND ESTERIFYING THE RESULTING CONDENSATE WITH THE POLYCARBOXYLIC ACID HALIDE.

United States Patent US. Cl. 260-455 R 7 Claims ABSTRACT OF THEDISCLOSURE Thiomethylenephenol compounds are provided wherein from twoto four hindered phenol radicals having thiomethyl substituents meta totheir hydroxy groups are joined, either directly or through interposedethoxy groups, to the carbonyl radicals of an organic polycarboxylicacid. These compounds have the formula:

OH CH3 wherein R is a branched chain alkyl group containing three toabout twelve carbon atoms, 2 is zero or one, n is 2, 3, or 4, and Y isthe residue of the organic carboxylic acid Y(CO0H),,. They areantioxidants for oxygen-sensitive organic materials, particularlypolyolefins of 2-6 carbon atoms such as polypropylene plastics. They areprepared by condensing from 2 to 4 moles of a 3-mercaptomethyl-Z,4-dimethyl 6 branched-chain alkylphenol with thechloride or bromide of an organic dicarboxylic, tricarboxylic ortetracarboxylic acid, preferably in the presence of an acid acceptor, orby first condensing the corresponding 3-chloromethylphenol withZ-mercapto ethanol and esterifying the resulting condensate with thepolycarboxylic acid halide.

This application is a continuation-in-part of application No. 5,089,filed Jan. 22, 1970, now abandoned.

This invention relates to thiomethylenephenol compounds wherein two ormore hindered phenol radicals are joined through thiomethyl groups tothe carbonyl radicals of organic polycarboxylic acids, either directlyor through interposed ethoxy groups. I have found that compounds of thisclass which have the chemical structures hereinafter defined can beprepared from readily available starting materials, and that they aregood antioxidants for organic materials subject to oxidativedeterioration when added thereto in antioxidizing amounts. My inventiontherefore includes the new compounds themselves, their methods ofpreparation, compositions of matter in which they are incorporated asantioxidants, and antioxidant processes in which they are used.

The new polycarboxylic acid-bridged thiomethylenephenols of my inventionare defined accurately by the formula 9 Ice In all of these compoundsthe thiomethylene-containing radical is meta to the hydroxyl group andis therefore not in conjugation therewith; this imparts good antioxidantand non-staining properties to the compounds. In addition the phenolichydroxyl is fully hindered by a methyl radical adjacent thethiomethylene substituent and by a larger secondary or tertiary alkyl ofat least three and preferably four or more carbon atoms on its oppositeside. This ensures the formation of antioxidants that arenondiscolon'ng, a very important property in an antioxidant forpolyolefins and other light colored synthetic and natural plastics.Representative branched-chain alkyls that may be present at the6-position of the phenol radical are isopropyl, isobutyl, tertiarybutyl, dimethylpropyl, tertiary octyl, 2,2-diethylhexyl, and diandtri-propylene and butylene radicals. Tertiary butyl is the preferredsubstituent.

The preferred compounds of my invention are those according to Formula Iin which n is 2 .and Y is a straightchain or branched-chain alkylene orthioalkylene of 2 to about 12 carbon atoms or a mononuclear aryleneradical of the formula (II) R1,

in which R R R and R are hydrogen or lower alkyl radicals, preferably offrom 1 to about 2 carbon atoms. Representative polycarboxylic acidswhich contain these radicals, and which may be used in the form of theirhalides to prepare compounds of Formula I, are succinic acid, glutaricacid, pimelic acid, dimethylglutaric acid, adipic acid, oxalic acid,malonic acid, suberic acid, azeleicacid, diphenic acid, maleic acid,fumaric acid, itaconic acid, sebacic acid, o-phthalic acid, isophthalicacid, terephthalic acid and alkyl-substituted phthalic acids such asmethylterephthalic acid, and 2,S-dimethyl-terephthalic acid,hexahydrophthalic acid, p-phenylenediacetic acid, and the like. Thethioldicarboxylic acids of the formula wherein n is a whole number from1 to 4 such as thiolpropionic acid are particularly important inpreparingantioxidants for polypropylene and other synthetic and naturalrubbers.

In addition to these preferred classes, halides of aromaticpolycarboxylic acids such as trimesic acid, trimellitic acid,pyromellitic, tricarballylic acid, aconitic acid, hemimellitic acid,naphthalene tetracarboxylic acid, etc., are useful.

The most readily available starting materials for preparing the phenolicmoieties of my new compounds are the corresponding2,4-dimethyl-6-secondary or tertiary alkylphenols; Haloinethylsubstituents such as the chloromethyl group .can be introduced into the3-position of these phenols by reaction with hydrochloric acid andformaldehyde or methylal in the presence of hydrochloric acid and H 50by the procedure of R. Wegler and E. Regel, reported in Makromol. Chem.9, 1 (1952). The 3-chloromethyl-2,4-dimethyl-6-sec. or tert.alkylphenols, prepared by this procedure, may then be reacted with2-mercaptoethanol or they may be converted into the corresponding3-mercaptomethyl-2,4-dimethyl-6-sec. or tert. alkylphenols by dissolvingthe chloromethyl compound in tetrahydrofuran, adding at least amolecular equivalent of an acid acceptor such as triethylamine,trimethylamine or anhydrous potassium carbonate and hub- 3 bling inhydrogen sulfide until the mercaptan formation is complete.

Reaction between the 3-chloromethyl-2,4-dimethyl-6- alkylphenol andZ-mercaptoethanol is preferably carried out in a mutual solvent such asmethyl isobutyl ketone, acetone or the like using a base such asanhydrous potassium carbonate as acceptor for the hydrochloric acidevolved. The reaction is most advantageously carried out under reflux,after which the mixture is cooled, acidified with hydrochloric acid, andthe organic layer is separated and washed with water. The solvent isthen removed by vacuum distillation, leaving the 2,6-dimethyl-3-hydroxy-6-alkyI-benzylthioethanol as an oily residue. From two to four moles ofthis material is used to esterify one mole of an organic dicarboxylic,tricarboxylic or tetracarboxylic acid, which is preferably reacted inthe form of its chloride or other acid halide by the proceduresdescribed and illustrated in the following examples.

The compounds of my invention in which two or more thiomethylenephenolgroups are linked directly to the carbonyl radicals of an organicpolycarboxylic acid are prepared by reacting the appropriate molarproportions of a 3-mercaptomethyl-2,4-dimethyl-6-sec. or tert.alkylphenol with the acid halide, preferably the chloride or bromide, ofthe organic acid in the presence of an acid acceptor such as pyridine orone of the other basic materials previously described. The reaction ispreferably carried out in a solvent such as tetrahydrofuran and atrelatively low temperatures on the order of 25 -50 C., and the productis recovered by acidifying the reaction mixture and extracting with avolatile solvent such as benzene. The product may be further purified bychromatography on silica or alumina gel, using a chloroformethyl acetateeluant.

It will thus be seen that my new process for the preparation of thecompounds of Formula I has as its essential feature the reaction of onemole of an organic polycarboxylic acid halide, preferably thechloride'or bro mide, with a stoichiometrically equivalent quantity(i.e. two, three or four moles, equal to the number of carbonyl groupsin the polycarboxylic acid) of a compound of the formula:

(III) in which R is a branched-chain alkyl of 3 to 12 carbon atoms and zis zero or one. This reaction is preferably carried out in the presenceof an acid acceptor capable of combining with the hydrochloric acidevolved and in a non-aqueous solvent such as chloroform, tetrahydrofuranand the like, and is continued until a polycarboxylic acid-bridgedthiomethylenephenol is obtained. The preferred process is one whereinthe chloride of an aliphatic dicarboxylic acid or thiolbisaliphaticcarboxylic acid of from 4 to about 14 carbon atoms or a mononucleararomatic dicarboxylic acid of from 8 to about 16 carbon atoms is used.

The compounds of this invention are especially useful as antioxidantsfor polyolefins (e.g., homopolymers or copolymers of mono a-olefins of2-6 carbons) in which they exhibit a high degree of activity and arenon-discoloring. The compounds can be similarly used in Other organicmaterial normally subject to oxidative deterioration, including ABS'resin's (acrylonitrile-butadiene-styrene copolymers), the polyamides,polyacetals (e.g., polyformaldehyde), polystyrene, impact polystyrene,natural rubber and the various synthetic rubbers includingethylene-propylene copolymer rubbers, and in oils, fats, greases,gasoline and the like.

The compounds are incorporated into the various substrates according toany of the Well known techniques,

including milling, Banbury mixing, swelling, etc. In polypropylene thecompounds are effectively incorporated by milling on a conventional tworoll plastic mill. The compounds are effective as antioxidants over arange of concentration of from about 0.01 to about 5%. In polypropylenethey are used preferably at a concentration of from 0.05 to 1%, based onthe weight of the substrate. These quantities are sometimes hereinafterdescribed as antioxidizing amounts of the antioxidant compound orcompound mixture.

In the case of polymers, after milling, during which other ingredientssuch as filler, plasticizers and light absorbers may be added, thepolymer composition is compression molded, cast, spun, injection moldedor extruded to a shaped article.

The antioxidant activity of the compounds of this invention inpolypropylene is greatly enhanced by concurrent use vvith esters ofthiodipropionic acid, well known secondary stabilizers forpolypropylene.

Oxidative deterioration of polypropylene and other similar oxidizableplastic materials is evident from the embrittlement which occurs onexposure to atmospheric oxygen. The extent to which the antioxidantprotects against deterioration is measured by determining the hours toembrittlement at C. C. when a specimen 1520 mils in thickness containingthe antioxidant, is exposed in a forced draft oven at this temperature.

The invention will be further described and illustrated by the followingspecific examples to which, however, it is not limited except as isindicated by the appended claims.

EXAMPLE 1 Bis[2-(4-t-butyl-3-hydroxy-2,6-dimethylbenzylthio) ethyl]terephthalate a )aC -CH:

l l CHz-S-CH2CHz0H c1-o--d-o1 l CHI (HsC)aC- CHI CH2.S.CH2CH:O.

I CH;

HaC C(CH=)$ CO.C|H4.CO.OCH2CH2.SCH

l CH3 To a 2 liter 3-neck flask, equipped with a Dean-Stark Trap,containing 900 ml. of methyl isobutyl ketone was added 189 g. (0.83mole) of 6-tert-butyl-3-chloromethyl- 2,4-dimethylphenol, 65 g. (0.83mole) of 2-mercaptoethanol, 115 g. (0.83 mole) of anhydrous potassiumcarbonate and 2 g. (.012 mole) of potassium iodide. The stirred mixturewas heated to reflux until the azeotropic distillation ceased. Themixture was cooled to 50 and added to 750 ml. of 0.61 N hydrochloricacid. The organic layer was separated and washed with four 200 ml.portions of water. The solvent was removed by distillation in-vacuo togive 217 g. (97%) of an oil residue.

A solution of 15.82 g. (.20 mole) of terephthaloyl chloride in 30 ml. ofchloroform was slowly added to a stirred mixture of 33.4 g. (.125 mole)of the 6-tertbutyl- 3- (Z-hydroxyethylthio) methyl]-'2,4-dimethylphenol,prepared as described above, and 15.82 g. (.20 mole) of pyridine in 130ml. of chloroform. The reaction was heated at 3540 for a period of 17 /2hours and cooled. The chloroform solution was washed with four 50 ml.portions of water, dried over anhydrous sodium sulfate and concentratedin-vacuo to give 44 g. of a tacky residue.

Successive recrystallizations from methanol and chloroform,respectively, gave an analytical specimen, colorless crystals, M.P.l42-l45.

Cale. :68.47, H=7.51, S=9.61. Found: 0:68.47, H=6.62, S=9.58.

EXAMPLE 2 Bis [4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-thio] ethyladipate aC)aC CH1 CH2- S CHzCHzO- To a mixture containing 26.8 g. (0.10mole) of 6-tertbutyl 3 [(2 hydroxyethylthio) methyl]-2,4-dimethylphenol,prepared as in Example 1, and 7.91 g. (0.10 mole) of pyridine in 100 ml.of tetrahydrofuran was added a solution containing 8.25 g. (.045 mole)of adipoyl chloride in 45 ml. of tetrahydrofuran. The mixture wasallowed to react at 30-35 for a period of 18 hrs. The pyridinehydrochloride (9.35 g.: theory 10.4 g.) was removed by filtration andthe filtrate concentrated to 50 ml. This was added to 200 ml. of coldWater to give an oily precipitate which was taken up in 200 ml. ofbenzene. The benzene solution was washed with 15% brine solution, driedover anhydrous sodium hydroxide to give 27.0 g. of an oil. The productwas purified by successive chromatography on silica gel using C'HCl-ethyl acetate (1:1), benzene-ethylacetate (1:2), benzene, respectively.A further chromatography on alumina using hexane-ethylacetate (2:1) gavea specimen whose nm-r results confirmed the assigned structure for thedesired compound.

EXAMPLE 3 Bis [4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-thio] ethylsuccinate The procedure of Example 2 was repeated but 6.97 g. (0.45 mol)of succinyl chloride was substituted for the adipoyl chloride. Theproduct was purified by chromatography and was obtained as a viscousoil.

'EXAMPLE 4 Tetrakis [2-(4-t.-butyl-3-hydroxy-2,6-dimethylbenzylthioethyl] pyromellitate To a mixture of 27 g. (0.10 mole) of6-tert-butyl-3- [(2 hydroxy ethylthio)methyl]-2,4-dimethylphenol, 12.6g. (.16 mole) of pyridine in 130 ml. of tetrahydrofuran was added asolution containing 6.6 g. (.02 mole) of pyromellitoyl chloride in 100ml. of tetrahydrofuran. The reaction was stirred at a temperature of3035 over a period of 12 hours and acidified with hydrochloric acid.

Evaporation of the solvent 'gave an oily residue which was taken up with300 ml. of benzene. The benzene solution was washed with water, driedover anhydous sodium sulfate, and concentrated to give 37 g. of an oilyresidue. This was purified by chromatography on alumina usinghexane-ethyl acetate (1:2) mixture to give a yellow oil. The structureof this product was supported by N.M.R. Spectroscopy.

'EXAMPLE 5 Bis [2-(4-tert-butyl-3-hydroxy-2,6-dimethylbenzylthio)ethyl]-2,S-dimethylterephthalate CH: J

Following the procedure of Example 4 but substituting the appropriatequantity of 2,5-dimethylterephthaloyl chloride for the pyromellitoylchloride, the above compound is produced.

EXAMPLE 6 Bis (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)- dithiol adipate0H OH CH S. C 0.(CH 4.00.8.CH1

I CH: CH:

To a 500 ml. 3-necked flask was added 26.88 g. (0.12 mole) of3-hydroxy-2,6-dimethyl-4-tert.butylbenzylmercaptan, and 11.86 g. (0.15mole) of pyridine in 115 ml. of tetrahydrofuran. A solution of 9.15 g.(0.05 mole) of adipoyl chloride in 25 ml. of tetrahydrofuran Was slowlyadded to the mixture with stirring, which was continued at about 25-35C. for 22 hours.

A 4.2 ml. portion of concentrated hydrochloric acid was diluted with 200ml. of water and added to the reaction mixture, which was then extractedwith two ml. portions of benzene. The benzene extracts were combined,washed twice with water, and concentrated to a syrupy residue. Theproduct, after purification by chromatography on silica gel using achloroform-ethyl acetate mixture, was obtained as colorless crystals.

EXAMPLE 7 Bis (4-t-butyl-3-hydroxy-2,G-dimethylbenzyl)- 3,3'-thiobis(thioldipropionate) a )a CH;

l CH:

CHzCHn. C 0. S .CHg

i CH1 To a 500 ml. 3-necked flask was added 26.88 g'. (0.12 mole) of3hydroxy-2,6-dimethyl-4-tert-butylbenzylmercaptan, 11.86 g. (0.15 mole)of pyridine in ml. of tetrahydrofuran. A solution of 10.75 g. (.05 mole)of 3,3-thiodipropionylchloride in 20 ml. of tetrahydrofuran was slowlyadded to the mixture with stirring. The reac tion was allowed to stir ata temperature of 30-5 over a period of 21 hours.

A 4.2 ml. portion of cone. hydrochloric acid was added to the reactionconcentrated and diluted by addition of 200 ml. of cold water. Theaqueous solution was extracted with two 100 ml. pertions of benzene. Thebenzene solution was washed with two 100 ml. portions of water andconcentrated to give 38 g. of a syrupy residue.

The product was purified by chromatography on silica gel using achloroform-ethyl acetate (4:1) mixture, and followed by a successivechromatography on silica gel using benzene as the eluant.Recrystallization from benzene gave an analytical specimen, colorlesscrystals, M.P. 124-5 Calcd: C=65.08; H=7.80; S: 16.27. Found: C=65.27;H=8.13; S= 16.22.

EXAMPLE 8 Bis(4-tert-butyl-3-hydr0xy-2,6-dimethylbenzyl)dithiolterephthalate O H CH3 C(C H03 (CH;)3G CHa &SCH

- CHz-S- C 43H:

A solution of 8.12 g. (.04 mole) of terephthaloyl chloride in 40 ml. ofbenzene was slowly added to a stirred mixture consisting of 22.4 g.(0.10 mole) of G-tert-butyl- 3-hydroxy-2,6-dimethylbenzyl mercaptan,39.6 g. (0.50 mole) of pyridine and 45 ml. of benzene. The reaction wasallowed to proceed for 12 hours at a temperature of 39-42".

The reaction mixture was added to 250 ml. of ice water containing 35 ml.(0.42 mole) of cone. hydrochloric acid to form a yellow oilyprecipitate. This was extracted with a 250 ml. portion of benzene. Thebenzene solution was washed with two 100 ml. portions of water, driedover anhydrous sodium sulfate, and concentrated to give 25 g. ofcrystallizate.

The crude product was recrystallized from a hexanebenzene-acetonitrile(11:6:1) mixture to give 12.98 g. of cream colored crystals, M.P.208-212. An additional recrystallization from benzene-hexane (1:2)mixture gave an analytical specimen, M.P. 215-218.

Calc: :70.59, H=7.27, :11.07. Found: C=70.14,

EXAMPLE 9 Bis 3-hydroxy-4-tert.butyl-2,6-dimethylbenzyl]dithiolisophthalate OH CH t.butyl I 0 t.butyl CH: JS-CH To a solution ofisophthaloyl chloride (5.07 grams, 0.025 mole) in 25 ml. of pyridine wasadded a solution of 3 hydroxy-4-tert.-butyl-2,6-dimethylbenzyl mercaptan(11.2 grams, 0.05 mole) in 35 ml. benzene containing 10 ml. pyridine.The mixture was refluxed for one hour, cooled and poured into water. Themixture was then acidified with concentrated hydrochloric acid,extracted with benzene and the combined benzene extracts washed withwater and dried. Removal of benzene gave 13 grams of crystals which wererecrystallized from methylcyelohexane to give 8.25 grams of a whitesolid, M.P. 206208 C.

8 EXAMPLE 1o Bis[ 3-hydroxy-4-( 1, 1 ,3,3-tetrametfl1ylbutyl)-2,6-dimethy1- benzyl]dithiolterephthalate OH OH t.octyl CH; H; t.octylCH CH3 To a mixture of 3-hydroxy-4-(1,1,3,3-tetramethylbutyl)2,6-dimethylbenzyl mercaptan (26 grams, 0.092 mole) and terephthaloylchloride (8.12 grams, 0.04 mole) in 150 ml. of benzene was addedpyridine (39.6 grams 0.50 mole) in 50 ml. of benzene. The temperaturewas maintained at 40 C. for 12 hours, the reaction mixture added to 35ml. of concentrated hydrochloric acid in 200 grams of ice, and theaqueous layer discarded.

The benzene layer was washed with three ml. portions of water,concentrated and the residue (31 grams) dissolved in 75 ml. of a mixtureof methanol-hexanechloroform (8:6:1). Seeding of the solution afforded11 grams of pale yellow crystals. Recrystallization from 55 ml. ofbenzene-hexane (1:4.5) gave 7.5 grams of pale yellow crystals, M.P.83-88".

EXAMPLE 11 Representative compounds of the present invention wereincorporated into unstabilized polypropylene in amounts of 0.2% on theweight of the polymer by milling at 175-l80 C. The polypropylene wasthen compression molded into films 15-20 mils in thickness. These wereaged in a forced-draft oven at C. and the efficiency of the compound asan antioxidant was determined by noting the time in hours toembrittlement at this temperature. The results are shown in thefollowing table.

1. A compound of the formula:

CHI

wherein R is a branched chain alkyl group containing three to about 12carbon atoms, n is 2, 3, or 4, and Y is an alkylene or thioalkylene of 2to about 12 carbon atoms or a mononuclear aromatic hydrocarbon radicalof the formula 9 wherein R R R and R are hydrogen or lower alkylradicals.

2. A compound as defined in claim 1 wherein R is tbutyl.

3. A compound as defined in claim 1 wherein Y is selected from the groupconsisting of m-phenylene, and p-phenylene and n is 2.

4. A compound as defined in claim 3 which isbis(4-tbutyl-3-hydroxy-2,6-dimethylbenzyl) dithiolterephthalate. 5. Acompound as defined in claim 3 which is bis(3-hydroxy-4-t-butyl-2,6-dimethylbenzyl)dithiolisophthalate. 6. A compoundas defined in claim 3 which is bis(3-hydroxy-4-t-octyl-2,6-dimethylbenzyl) dithiolterephthalate.

7. A compound as defined in claim 3 which is bis(4-tbutyl3-hydroxy-2,6-dimethylbenzy1)-3,3'-thiobis(thioldipropionate) UNITEDSTATES PATENTS 3,260,756 7/1966 OShea ct a1 260-455 A 3,260,736 7/1966Martin et a1 20-455 A 3,422,059 1/ 1969 Taylor et a1. 260-473 S3,553,158 1/1971 Gilfillan 260-4585 R 3,459,704 8/1969 Brooks et a1.260-45.85 R

FOREIGN PATENTS 426,332 3/1967 Japan 260-455 A LEWIS GOTI'S, PrimaryExaminer D. R. PHILLIPS, Assistant Examiner US. Cl. X.R.

